IT9022117A1 - PREPARATION OF SILICON OXYCARBON GLASS FROM COLLOIDAL SILICA TREATED WITH SILOXANOLS - Google Patents

Description

DESCRIPTION of the industrial invention

The present invention relates to glass compositions and in particular glass compositions comprising silicon, oxygen and carbon made from a colloidal silica treated with siloxanols.

Vitreous silica is a refractory glass, however, it devittifies at around 1100 ° C. Devitrification consists of the transition from the random structures of which glasses are made to a crystallized structure. Crystallization drastically reduces one of the predominant attributes of vitreous silica, namely its low thermal expansion and also several of its other desirable properties. As a result, much research has been directed at increasing the devitrification resistance of silica glass compositions.

Reactions between silicon, carbon and oxygen have been studied extensively. Known reactions in a system consisting of carbon and oxygen silicon contain oxygen combined with silicon to form silica, predominantly as silicon dioxide. At temperatures above 1100 ° C, silica begins to crystallize to form cristobalite, one of the common mineral forms of silica. Carbon can react with silicon to form crystalline silicon carbide or it can react with oxygen to form carbon monoxide.

The thermodynamics of reactions between silicon, carbon and oxygen is discussed in "The High Temperature Oxidation, Reduction, and Volatilization Reactions of Silicon and Silicon Carbide", by Gulbransen, E.A. and Jansson, S.A. Oxidation of Metals, Volume 4, No 3, 1972 . Thermodynamic analysis by Gulbransen et al shows that at 1200 ° C silica and carbon would form gaseous silicon monoxide and carbon monoxide or solid silicon carbide, SiC. However, it would not be expected to form a single material containing all and three elements. Gulbransen et al conclude that silica was not recommended for use in reducing atmospheres above 1125 ° C due to the formation of gaseous silicon monoxide. Again, silicon carbide was not recommended for use in environments containing oxygen due to the oxidation of silicon carbide.

There is a material described as carbon-modified vitreous silica and referred to here as "black glass" where 1 to 3% carbon has been added to the silica. The method of making black glass is described by Smith et al in U.S. Patent No. 3,378,431. Carbonaceous organic substances such as carbowax are added to the silica and the mixture is hot pressed at about 1200 ° C to form black glass. Smith, C.F. Jr featured black glass for infrared spectroscopy in "The Vibrational Spectra of High Purity And Chemically Substituted Vitreous Silicas," Alfred University graduation thesis, Alfred New York, May 1973. Smith reveals that in addition to elemental carbon dispersed in black glass , a certain amount of carbon is associated with oxenon in carbonate-type groups. The term carbonate describes a radical having one carbon atom bonded to three oxygen atoms and having the structure,

The mechanical strength of black glass is similar to the strength of conventional carbon-free silica glass, however black glass has a higher resistance to devitrification than conventional silica glass which begins to devitrify at around 1100 ° C, while black glass begins to devitrify. to devitrify at about 1250 ° C. The higher thermal stability of black glass allows it to be used at higher temperatures where conventional silica would devitrify.

In a commercially produced continuous silicon carbide ceramic fiber sold under the "Nicalon" brand, approximately 10% oxygen is introduced into the fiber to crosslink it. After crosslinking, the fibers are pyrolyzed and oxygen is believed to become part of the fiber as an amorphous contaminant, possibly in the form of silica. The degradation behavior of these fibers after heat treatment in various environments was reported in the article "Thermal Stability of SiC Fibers (Nicalon)", Mah, T. et al., Journal of Material Science, Vol. 19, pages 1191 to 1201 (1984). Mah et al found that regardless of the environmental conditions during heat treatment, the strength of the "Nicalon" fiber decreased when the fibers were subjected to temperatures greater than 1200 ° C. The degradation of the fibers was associated with loss of carbon monoxide from the fibers and with growth of beta silica carbide grains in the fibers.

Ceramic materials generally exhibit a brittle behavior characterized by their high strength and low fracture strength. Fracture strength is the resistance to the propagation of cracks in materials. The development of ceramic compounds has been investigated as a way to alleviate the brittle behavior of ceramics. "Nicalon" is an excellent ceramic fiber but degrades at temperatures above 1200 ° C.

Integrating "Nicalon" fibers into a protective ceramic matrix having desirable mechanical properties and capable of withstanding temperatures substantially greater than 1200 ° C would be one way to form an improved ceramic compound. However, from the foregoing discussion, it is evident that the properties of known ceramics or glasses and especially those containing silicon oxygen and carbon, are degraded for example by decomposition of silicon carbide or devitrification of conventional glass.

Therefore, an object of this invention is to form an amorphous glass, comprising silicon, oxygen and carbon in which substantial portions of the carbon atoms are chemically bonded to silicon atoms and the remaining carbon is elemental carbon dispersed in the glass matrix. Such glass compositions resist decomposition in oxidizing or reducing atmospheres and devitrification at temperatures up to about 1600 ° C.

Another object of this invention is to provide a process for forming a glass comprising silicon, oxygen and carbon by pyrolyzing silicas colfoidal treated with siloxanols.

Yet another object of the invention is to form glass objects from a colloidal silica treated with a siloxanol.

It has been found that colloidal silicas treated with siloxanols can be pyrolyzed in a non-oxidizing atmosphere to form unique glass compositions. Surprisingly, it has been found that colloidal silicas treated with pyrolyzed siloxanols in a non-oxidizing atmosphere below about 1600 ° C do not form silica, cristobalite, silicon carbide, carbon monoxide, or mixtures of silica and elemental carbon.

The substantially stable non-crystalline glasses of this invention are made by pyrolyzing a colloidal silica treated with an oxide to form a glassy composition, comprising silicon, oxygen and carbon in which a major portion of the carbon atoms are chemically bonded to silicon atoms. These glasses resist crystallization and decomposition into oxidizing and reducing atomospheres at temperatures up to about 1600 ° C. In addition, a major portion of the carbon present in the glasses of this invention is bonded to silicon, where the remainder is present as elemental carbon dispersed within the glass matrix, so that there are no detectable carbonate groups.

The bonds between carbon and oxygen discovered in the glasses of this invention were previously unknown in silica glasses. In silica glasses and especially black glass, carbon has only been known to be present in the form of an unbound element in the silica matrix or carbonate groups, where carbon is bound with oxygen. The glasses of this invention, characterized by the chemical bond described above, are hereinafter referred to as silicon oxycarbon glasses.

Glasses of this invention are produced from a colloidal silica treated with siloxanols heated in a non-oxidizing atmosphere to pyrolyze the treated silica. As used herein, the term, non-oxidizing atmosphere, means an atmosphere essentially devoid of oxygen that removes pyrolysis by-products from the pyrolyzing resin without affecting the reactions that occur during pyrolysis. Examples of non-oxidizing atmospheres include a vacuum lower than approximately 10 4 atmospheres (0.1013 mbar), inert atmospheres such as helium, argon or nitrogen, and reducing atmospheres, such as hydrogen.

As stated here, a colloidal silica treated with siloxanols comprises a dispersion of colloidal silica in a partial condensate of a silanol of the formula RSi (OH) 3. The partial condensate is formed by hydrolysis of an organotryalkoxysilane in which R is a monovalent hydrocarbon radical containing from about 1 to 12 carbon atoms, such as a halohydrocarbon, a C (1-12) alkyl, a C (6-12) 0 aryl an ester such as a methacrylate or acrylate; at least 70% by weight of the silanol being methyltrihydroxy silane. The partial condensate of silanol is siloxanol. Colloidal silica treated with siloxanol is sometimes referred to herein as treated silica or treated colloidal silica.

The pyrolysis of the treated silica forms a silicon oxycarbon glass which is characterized by a continuous breakdown of electrons between silicon, oxygen and carbon atoms. In silicon oxycarbon glass, silicon atoms are present in up to four polyatomic units. In a unit, here called tetraoxysilicon, one silicon atom is bonded to four carbon atoms. In a second unit, here called monocarboosiloxane, a silicon atom is bonded to three oxygen atoms and one carbon atom. In a third unit, here called dicarboosiloxane, a silicon atom is bonded to two oxygen atoms and two carbon atoms. In a fourth unit, here called tetracarbosiiicon, a silicon atom is bonded to four carbon atoms. When a treated silica formed from the partial condensate of methyltrimethoxysilane and colloidal silica in a ratio of 1.8: 1 is pyrolyzed, a silicon oxycarbon glass is formed having a distribution of polyatomic units comprising, from about 76 to 86% in weight of tretraoxysilicon, from about 12 to 21% by weight of monocarboosiloxane and up to about 8% by weight of dicarboosiloxane, with at least about 3% by weight of elemental carbon dispersed within the glass matrix. Polyatomic units are mainly bonded by silicon-oxygen bonds with a small and insignificant number of bonds between carbon and oxygen atoms.

The following description of the invention will be more easily understood by referring to the patent figures described below.

Figure 1 is a graph showing the weight loss during pyrolysis of a colloidal silica treated with siloxanol.

The figure is a graphical representation of the silicon nuclear magnetic resonance spectrum 29 of silica oxycarbon glass formed by pyrolyzing a colloidal silica treated with a siloxanol.

Figure 3 is a graphical representation of the nuclear magnetic resonance spectrum of silicon 29 silicon carbide "Nicalon".

The glasses are generally formed from an extremely viscous supercooled liquid and possess a polymerized network structure with short distance order. The glasses of this invention are not made from super cooled liquids, but possess a network structure with short distance order. Instead of supercooling a liquid, the glasses of this invention are formed by pyrolyzing a colloidal silica treated with siloxanol in a non-oxidizing atmosphere. However, the glasses of this invention have the short distance sorting feature of conventional glasses.

The colloidal silica treated with siloxanol which can be used in the practice of the present invention comprises a dipsersion of colloidal silica in the partial condensate of a stianol of the formula RSi (OH) 3, where R is a monovalent hydrocarbon radical having from about 1 to 12 atoms of carbon such as a halohydrocarbon, a C (1-12) alkyl, a C (-612) 'aryl, or an ester such as a methacrylate or acrylate; at least 70% by weight of the stianol essedo methyltrihydroxy silane. A colloidal silica treated with the partial condensate can be dried to form a powder, or the treated silica can be diluted in a solution of aliphatic alcohol and water containing about 10 to 50% by weight of solid parts, the solid parts essentially consisting from 10 to 70% by weight of colloidal silica and from 30% to 90% by weight of the partial condensate, the composition having a pH of 3.5 to 8.0.

The treated colloidal silica can be prepared by hydrolyzing a trialkoxysilane or a mixture of trialkoxysilanes of the formula RSi (OR ') 3, in which R is as previously defined, and R' is an alkyl radical in the presence of an aqueous dispersion of colloidal silica.

Suitable aqueous dispersions of colloidal silica generally have particle sizes from 5 to 150 millimicron in diameter. These silica dispersions are known in the art and those commercially available include, for example, those sold under the brand names of Ludox (DuPont) and Nalcoag (NALCO Chemical Co.). Such colloidal silicas are available as acidic and basic hydrosols. Colloidal silicas having an average particle size of 5 to 25 millimicrons are preferred. A particularly preferred one for the present purposes is known as Ludox AS-40, sold by the DuPont Company.

In preparing the treated colloidal silica composition, the aqueous dispersion of colloidal silica is added to an alkyltrioalkoxysilane or an aryltrialkoxysilane which may contain a buffering agent, such as acetic acid, alternatively alkitriacetoxysilane can be used in place of the alkoxysilanes as acid. If desired, small amounts of dialkidyalkoxysilane can also be used in the reaction mixture. The temperature of the reaction mixture is maintained between about 20 ° C and about 40 ° C and preferably below 25 ° C. It was found that in about 6 to 8 hours sufficient trialkoxysilane reacted to reduce the initial two-phase liquid mixture to a single liquid phase in which the silica is dispersed.

In general, the hydrolysis reaction is allowed to continue for a total of about 12 to 48 hours, depending on the desired viscosity of the final product. The longer the hydrolysis reaction is allowed to continue, the higher the viscosity of the colloidal silica dispersion will be.

After the hydrolysis has been completed, the solids content is adjusted by adding alcohol, preferably isopropanol, to the dispersion of colloidal silica. Other suitable alcohols for this purpose include lower aliphatic alcohols such as methanol, ethanol, isobutanol, isopropanol, n-butyl alcohol and t-butyl alcohol or mixtures thereof. When it is desired to use a treated colloidal silica in which the partial condensate is in solution, the solvent system may contain from about 20 to 75% by weight of alcohol.

The pH of the resulting reacted composition is in the range of about 3.5 to 8.0, preferably about 6.6 to about 7.8 or 3.8 to 5.7. If necessary, a dilute base, such as ammonium hydroxide, or a weak acid, such as acetic acid, can be added to the composition to adjust the pH to the desired range.

The acid is used to buffer the basicity of the initial reaction mixture in two liquid phases and therefore also moderate the degree of hydrolysis. Glacial acetic acid and also other acids such as organic acids such as propionic, butyric, citric, benzoic, formic, oxalic and the like can be used. Alkyltriacetoxysilanes of which the alkyl group contains 1 to 6 carbon atoms can be used, alkyl groups having 1 to 3 carbon atoms being preferred. Most preferred is trimethyltriacetoxysilane.

The silantriols, RSi (OH) ^, indicated above, are formed as a result of the hydrolysis of the corresponding trialkoxysilanes with the aqueous medium, i.e. the aqueous dispersion of colloidal silica. Exemplary tryalkoxysilanes are those containing methoxy, ethoxy, isopropoxy and n-butoxy substituents which, by hydrolysis, form silantriol and the corresponding alcohol; If a mixture of trialkoxysilanes is used, a mixture of different silylantriols is produced, as well as of different alcohols. Following the production of silantriol or mixtures of silantriols in the basic aqueous medium, condensation of the hydroxyl substituents occurs to form the bond

The non-volatile solid portion of the treated colloidal silica is here a mixture of colloidal silica and the partial condensate, or siloxanol, of a silanol. The major portion or all of the partial condensate or siloxanol is obtained from the condensation of methyltrihydroxysilane and, depending on the introduction of ingredients into the hydrolysis reaction, minor portions of the partial condensate can be obtained, for example, from the condensation of methyltrihydroxysilane with ethyl trihydroxy silane or propyltrhydroxy silane. ; methyltrihydroxysilane with C6H5Si (OH) 3, or mixtures of the above. It is preferred to use all methyltrimethoxysilane, producing all methylsilantriol, in preparing processed colloidal silica compositions which can be dried to form a powder or dissolved in a solvent so that the partial condensate is present in an amount between about 55 and 75% by weight of the solids. totals in a cosolvent of alcohol and water, the alcohol forming about 50 to 95% by weight of the cosolvent.

The silicon oxycarbon glass is formed by pyrolysis of colloidal silica treated with siloxanol in a non-oxidizing atmosphere at temperatures between 900 and 1600 ° C. Preferably, the degree of heating during pyrolysis is controlled to allow the pyrolysis byproducts to unfold without leaving voids or bubbles in the silicon oxycarbon glass.

Preferably, heating rates lower than about 1 ° C per minute are used. During pyrolysis, byproducts unfold and cause weight loss as the treated silica thickens. Although the pyrolyzed treated silica undergoes a weight loss, the density of the pyrolyzed treated silica is increased due to a reduction in volume of the same pre-treated treated silica. The pyrolysis reactions are essentially complete when a substantially constant weight has been obtained in the pyrolyzed treated silica. A substantially constant weight is generally obtained between about 900 and 1250 ° C. Further thickening of the pyrolyzed treated silica can happen after the weight loss is over if you continue heating. However, it may be desirable to stop heating and pyrolyzing of the treated silica after it has been fully thickened, in other words, the reduction in volume is stopped. The weight loss during pyrolysis of a treated silica was determined to be about 14 percent. The glasses of this invention resist devitrification and remain structurally stable at temperatures up to at least 1600 ° C. The term "Structurally stable" refers to a bulk material which essentially maintains the same microstructure from room temperature up to about 1600 ° C. The formation of small crystallized zones up to about 100 Angstroms in an otherwise amorphous matrix has substantially no adverse or detrimental effects on the properties of the bulk material. Therefore, structurally stable glasses of the present invention are essentially amorphous, but may contain small crystallized zones of, for example, graphite, cristobalite, or silicon carbide within the glass, or show minor amounts of cristobalite on the glass surfaces.

Silicon oxycarbon glass objects can be formed by pulverizing the pyrolyzed treated silica into a powder using abrasive wheels known in the art. The silicon oxycarbon powder is then consolidated by hot pressing to form an object. One way to hot pressing is to apply an axial pressure of at least about 34.45 MPa (5 ksi) at about 1550 ° C to 1600 ° C to the powder. The ksi unit is the equivalent of 1000 pounds per square inch. Such pressures and temperatures are sufficient to form a thickened object.

Shaped objects can also be formed directly from the treated silica. First the treated silica is dissolved in a solvent, such as isopropanol and then poured into a desired shape. Illustrative of the solvents which have been found suitable for bringing the silica into solution are lower aliphatic alcohols such as methanol, ethanol, isobutanol, n-butyl alcohol and t-butyl alcohol or their mixtures, or preferably isopropanol. Treated silicas can be dissolved in about 20 to 75% by weight of solvent.

The cast treated silica is dried at room temperature and slowly pyrolyzed in a non-oxidizing atmosphere, as described herein. Pyrolysis is performed at a low heating rate which avoids the formation of voids and bubbles when gas is unwound and causes a weight loss in the treated silica. When the weight of the pyrolyzed treated silica stabilizes, the pyrolysis is complete. Alternatively, the treated silica, which is normally in the form of a powder, can be shaped by hot pressing.

Silica treated in isopropanol solution can also be pulled into fibers. The treated silica solution is treated with a base such as ammonium hydroxide to increase viscosity to a point where a solid object can be dipped into the solution and withdrawn, pulling a strand of treated silica from the solution. Fibers can then be sucked or pulled from the treated silica solution by such dipping processes. Alternatively, the treated silica solution can be sucked into a Teflon tube with a slight vacuum. Given the isopropanol evaporates and the treated silica solution increases in viscosity, the fiber shrinks and is pulled out of the tube. Fibers are strengthened for easier handling by heating them to approximately 50 ° C. The fibers are then pyrolyzed in a non-oxidizing atmosphere or in a vacuum, as described above.

Ceramic composites having ceramic fibers in a silicon oxycarbon and ceramic filler glass matrix can be formed. The treated silica is dissolved in a solvent and the ceramic particles are dispersed in the solution to form an infiltrating slurry. The ceramic particle filler controls the shrinkage of the compound matrix during pyrolysis and can be chosen so that the matrix is compatible with the fiber reinforcement to be used. Some examples of ceramic fillers are powdered silicon carbide diatomaceous earth and 2SiO2Al2O3 aluminosilicate called munite. A ceramic fiber or fibers, or a cloth of the fibers is drawn through a stirred bath of the infiltrating slurry. Some examples of ceramic fibers are carbon fiber, silicon carbide fiber, and aluminoborosilicate fibers. The impregnated fiber is then shaped and dried to allow evaporation of the solvent. One shaping method comprises wrapping a spiral impregnated fiber onto a drum to form a panel. Fiber layers can be consolidated by applying heat and pressure to form a continuous matrix of treated silica surrounding the ceramic fibers. The composition is then pyrolyzed in a non-oxidizing atmosphere or in a vacuum, as described above. The treated silica densifies into a substantially amorphous glass of silicon oxycarbon which binds the ceramic filler, thus forming a continuous matrix around the fibers. Depending on the pyrolysis temperature used, the ceramic filler can be dispersed, partially sintered or completely sintered within the glass.

Optionally, the ceramic composite can be reinfiltered with the infiltrating slurry to reduce porosity in the composite. The composite is placed in the re-infiltrating solution under vacuum. Pressure is applied to the solution to push the solution into the pores of the composite. After re-infiltration, the solvent is allowed to evaporate and the re-infiltrated composite is pyrolyzed in a non-oxidizing atmosphere or in a vacuum, as described above. Reinfiltration and pyrolysis can be repeated as many times as necessary to achieve the desired degree of density in the matrix.

The amorphous silicon oxycarbon glass matrix binding a ceramic charge surrounds and protects the ceramic fibers from decomposition in oxidizing and reducing atmospheres at temperatures up to about 1600 ° C. It has been found that the inert nature of silicon oxycarbon glass readily accepts ceramic fibers without reacting with them and degrading their properties. As a result, a silicon oxycarbon glass containing ceramic fillers can be used as the matrix material for several known ceramic fibers.

The following examples are offered to further illustrate the silicon oxycarbon glass of this invention and methods of making the glass and glassware.

EXAMPLE 1

The siloxanol-treated colloidal silica composition comprising the partial condensate derived from methyltrimethoxysilane and colloidal silica in a weight ratio of 1.8: 1 was pyrolyzed while the weight loss from the treated silica was measured by thermogravimetric analysis. Thermogravimetric analysis is a method of measuring weight losses from a sample as it is heated. The material was pyrolyzed in a hydrogen atmosphere by heating it at a rate of 10 ° C per minute up to a temperature of 1250 ° C. The measured weight loss of silicon oxycarbon formed after pyrolysis was approximately 14 percent.

The pyrolysis weight loss data of the treated silica are presented in the graph of figure 1. In the graph of figure 1, the percentage weight loss in the sample is plotted on the ordinate, while the heating temperature increase is plotted on the abscissa. The graph of figure I shows that the weight loss is essentially complete in the sample at about 900 ° C. Substantially no evidence of crystallization by X-ray diffraction of the pyrolyzed material was found.

The composition of different glasses can be broadly defined by referring to the amount of each element in the glass. However, it is the order at a short distance in the glasses that gives them their different properties. Therefore, by characterizing the short-distance sorting in glasses, different compositions of glass can be defined with respect to properties. The short-distance ordering of the silicon oxycarbon glass prepared in Example 1 is determined by defining the percentage of each of the polyatomic units; monocarboosiloxane, dicarboxiloxane and tetraoxysilicon which are present in the glass.

the solid state silicon nuclear magnetic resonance spectrum 29 of the silicon oxycarbon glass prepared above was recorded and is presented in Figure 2. Figure 3 is the nuclear magnetic resonance spectrum of silicon 29 from a sample of carbide fibers of "Nicalon" silicon. The radiation intensity measured by the cited sample is plotted on the ordinate of Figures 2 and 3 and the parts per million (ppm) of chemical displacement from a tetramethyl silicon standard that fixes the point are plotted on the abscissa of zero of the abscissa. Chemical shifts in ppm are known for several polyatomic units, for example tetraoxysilicon, dicarbosiloxane and monocarbosiloxane are shown in 'NMR Basic Principles and Progress 29SNMR Spetroscopic Results ", editors P. Diehl, R. Kosfeld, Springer Verlag Berlin Heidelberg 1981 on pages 186, 184 and 178. Thus each peak in Figures 2 and 3 defines the short-distance ordering of particular polyatomic units of silicon.

The spectrum of the silicon oxycarbon glass of Figure 2 'contains peaks indicated from 1 to 3. Peak 1 is dicarboosiloxane, the small one is monocarboosiloxane and the peak 3 tetraoxysilicon. By integrating the area under each peak, the fraction of each of these polyatomic units that is present in the glass can be determined. A correction for background interference was made to the spectra of Figures 2 and 3 before determining the integrated area under each peak.

The integrated area under each peak of Figure 2 reveals a composition for the silicon oxycarbon glass prepared as described above comprising, up to about Γ8% by weight of dicarboosiloxane, from about 11% to 21% by weight of monocarboxiloxane. and about 76 to 86% by weight of tetraoxysilicon. The analysis of the nuclear magnetic resonance spectra and the black appearance of the glass indicate that at least about 3% by weight of elemental carbon is atomically dispersed in the glass or in small clusters.

Treated colloidal silicas having various ratios of siloxanol to colloidal silica can be pyrolyzed to form silicon oxycarbon glasses. Processed colloidal silicas having a siloxanol to colloidal silica ratio that is greater than 1.8: 1 are expected to have a lower tetraoisilicon content which is in the lower end of the 76 to 86% range described above, or more in low. Conversely, treated colloidal silicas having a siloxanol to colloidal silica ratio that is less than 1.8: 1 are expected to have a higher tetraoxysyl content, which is in the upper part of the range from 76 to 86% or more.

The spectra of Figure 2 can be compared to the silicon carbide spectra of Figure 3 measured from a sample of "Nicalon" silicon carbide fiber. The composition for "Nicalon" of figure 3 in percentage by weight, is about 68% of silicon carbide, about 8% of dicarboosiloxane, about 17% of monocarboosiloxane and about 7% of tetraoxysilicon. In the spectra of figure 3 it can be seen that the fibers of "Nicalon" are mainly formed of silicon carbide with minor amounts of carboxy-siloxane, monocarboxy-siloxane and tetraoxysilicon. In contrast, the spectra of FIG. 2 show that silicon oxycarbon glass is formed from substantial amounts of dicarboosiloxane, monocarboosiloxane and tetraoxysilicon. This unique short-range ordering of silicon oxycarbon glass which binds carbon to silicon in a way previously unknown in glass provides the greatest resistance to devitrification and decomposition and characterizes the glasses of this favention.

The composition of the silicon oxycarbon glass sample and the Nicalon sample can also be described by considering the mol percent of each polyatomic unit. Table I below provides the conversion between mol percent and weight percent of each of these compositions.

The mol percent gives the percentage of each polyatomic unit in the samples on a molecular basis. The percentage of silicon atoms in the samples that is bonded to oxygen or carbon can be determined using the percentages in moles. The silicon oxycarbon glass sample from example 1, has from about 16 to 26% of silicon atoms of the glass bonded to at least one single carbon atom. The "Nicalon" silicon carbide sample has about 90 to 100% of the silicon atoms in the sample bonded to carbon.

Claims (4)

CLAIMS 1. A process for forming a glass composition comprising: pyrolyzing a colloidal silica treated with siloxanols in a non-oxidizing atmosphere by heating for a period of time sufficient to form a silicon oxycarbon glass which remains structurally stable at temperatures up to 1600 ° C. 2. A process for forming a glassy composition, comprising: partial with respect to colloidal silica and about 1.8: 1. 10. Glass composition comprising silicon oxygen and carbon chemically bonded with the glass substantially free of chemical bonds between oxygen and carbon atoms; the glass being produced by a process comprising pyrolyzing a colloidal silica treated with siloxanol in a non-oxidizing atmosphere by heating for a period of time sufficient to form a silicon oxycarbon glass which remains structurally stable at temperatures up to 1600 ° C. 11. Glass composition comprising silicon, oxygen and carbon chemically bonded with the glass substantially free of chemical bonds between oxygen and carbon atoms; the glass being produced by a process comprising pyrolyzing a colloidal silica treated with siloxanol in a non-oxidizing atmosphere by heating for a period of time sufficient to form a silicon oxycarbon glass which remains structurally stable at temperatures of about 1250 ° C or more . The glass of claim 11, wherein said colloidal silica treated with siloxanol is a dispersion of colloidal silica, having particle size between about 5 and 150 millimicrons in a partial condensate of a siloxanol of formula RSi (OH) 3, where R is a monovalent hydrocarbon radical having from 1 to 12 carbon atoms. 13. The process of claim 11, wherein said colloidal silica treated with siloxanol is a dispersion of colloidal silica, having particle size between about 5 and 150 millimicrons, in a partial condensate of a silanol of the formula RSi (OH) 3, where R is a methyl group. 14. The glass of claim 11, wherein said partial condensate is pyrolyzing a colloidal silica treated with siloxanols in a non-oxidizing atmosphere, heating for a period of time sufficient to form a silicon oxycarbon glass which remains structurally stable at temperatures of 1250 ° C or more. 3. The process of claim 2, in which pyrolysis is obtained by heating from about 900 to 1600 ° C. The process of claim 3, in which heating is carried out for a period of time ending when the weight loss from the pyrolyzed treated colloidal silica substantially stabilizes. 5. The process of claim 3, in which heating is carried out for a period of time which allows the treated silica to thicken completely. 6. The process of claim 2, in which pyrolysis is carried out in a gaseous hydrogen atmosphere. 7. The process of claim 2, wherein said oxide-treated colloidal silica is a dispersion of colloidal silica, having particle sizes between about 5 and 150 miliimicrons in a partial condensate of silanol in the formula RSi (OH) 3, where R is a monovalent hydrocarbon radical having from 1 to 12 carbon atoms. 8. The process of claim 2, wherein said colloidal silica treated with siloxanol is a dispersion of colloidal silica having particle size between about 5 and about ISO miliimicron in a partial condensate of a siloxanol of formula RSi (OH) 3, where R is a methyl group. 9. The process of claim 7 wherein said partial condensate is formed by hydrolysis of methyltrimethoxysilane and the ratio of condensate formed by hydrolysis of methyltrimethoxysilane and the ratio of partial condensate to colloidal silica is about 1.8: 1. 15. Glass that remains structurally stable at temperatures of about 1250 ° C or more, comprising polyatomic units of silicon, oxygen and carbon in percent by weight of about 11 to 21% monocarboosiloxane, up to about 8% dicarboosiloxane, from about 76 to 86% tetraoxysilicon, with at least about 3% elemental carbon dispersed in the glass. 16. A glass which remains structurally stable at temperatures up to about 1600 ° C, comprising polyatomic units of silicon, oxygen and carbon, in percentage by weight, from about IM I to 21% monocarboosiloxane, up to about Γ8% dicarboosiloxane, about 76 to 86% tetraoxysilicon, with at least about 3% elemental carbon dispersed in the glass. 17. Glass that remains structurally stable at temperatures of about 1250 ° C, comprising silicon, oxygen and carbon in a mass of silicon oxycarbon glass, in which about 16 to 26% silicon atoms are bonded to at least a single carbon atom.